We don't need no DIC libs / we don't need no deps control

rollyourown.php

<?php
// Context: I'm trying to argue that DI (and DIC) are great, and DIC libs suck. 
// Happy to be proven wrong!

final class Router {
    private $dependencies;
    public function __construct (Dependencies $dependencies) {
        $this->dependencies = $dependencies;
        // You might say that this is Service Locator, but it's not. This router is toplevel,
        // and toplevel must have access to dependencies. After that it can all just bubble nicely using proper DI.
    }
    public function route(Command $cmd) {
        switch(true) {
            case $cmd instanceof RubPlumbus:
                $this->dependencies->PlumbusRubber()->handle($cmd);
                break;
            case $cmd instanceof SpitOnPlumbus:
                // $this->dependencies->SomeOtherService()->handle($cmd);
                //.. etc
        // So what it's just a dumb list of case and instanceof instead of clever autowiring. This takes no time to
        // write and no time to understand and nobody will ever need to stackoverflow it to get it.
        // This is all lazy by default, Dependencies only makes stuff we ask for and we only ask for stuff when we need
        // it.
        // For content based routing:
            case $cmd instanceof PaintPlumbus:
                if($cmd->isBlue()) {
                    echo "it's blue";
                    // do specific blue stuff
                } else {
                    // ...
                }
                break;
        }
    }
}

abstract class Dependencies {

    private $environment;

    function __construct (Environment $environment) {
        // No dependency on a global mutable env, this is a value object.
        $this->environment = $environment;
    }

    public function PlumbusRubber (): PlumbusRubber {
        // Public, because this service is toplevel
        return new PlumbusRubber($this->PlumbusRepository());
    }

    // Only the methods above this line are public, because I expose as few of them as possible to the outside. I'm not
    // just letting you get any dep from anywhere. Symfony has this feature, but it's public by default there, which
    // annoys me. I'm easily annoyed by public things that shouldn't be public.
    
    protected function PlumbusRepository (): PlumbusRepository {
        return $this->MySQLPlumbusRepository();
    }

    protected function MySQLPlumbusRepository (): MySQLPlumbusRepository {
        // NOTE: Private! Never exposed outside
        return new MySQLPlumbusRepository($this->DBConnection());
    }

    protected function DBConnection (): DBConnection {
        // The others deps didn't sharing because they're stateless and fast and often only used once in a request.
        // Here there is some side effect on instantiation so it makes sense to reuse

        $environment = $this->environment;
        return
            $this->share(
                __METHOD__, // used as key
                function () use ($environment) {
                    return new DBConnection(
                        $environment->db_host(),
                        $environment->db_username()
                    /* ... */
                    );
                }
            );
    }

    private $shared = [];
    protected function share ($key, callable $factory) {
        // I sure wish PHP had generics :`-(
        if ( ! array_key_exists($key, $this->shared))
        {
            $this->shared[$key] = $factory();
        }

        return $this->shared[$key];
    }
}

final class ProductionDependencies extends Dependencies {
}
final class StagingDependencies extends Dependencies {
    // A typical use case would be to have a mock Mailer so we can't send email from tests
}
final class TestingDependencies extends Dependencies {
    // Overriding stuff we want to differently in unit tests
    protected function PlumbusRepository (): PlumbusRepository {
        return $this->InMemoryPlumbusRepository();
        // Or use your favourite mocking lib if you must
    }
}

// Benefits:
//  * No XML! No YAML! No frameworks! Just plain old POPOs and tautologies!
//  * No black magic autowiring
//  * All in glorious typehinting
//  * I can even write unit tests for the Dependencies class itself.
//  * There is no naming convention you have to learn like "app.thing.some_underscord_thing". Methods are named
//    after the interface or the class of the thing they return. Such easy, much wow.
//  * I don't need IDE plugins to navigate the xml shit and detect missing services because it's all POPO!
//  * If you think any of this involves work: it's less work than any DIC lib I've used, because it's the same amount
//    of information as you'd have to write anyway with whatever configuration format they use. The only exception is
//    autowiring, but you'll pay that back with itnerest in debugging time anyway.

// ignore below, just making all the GLORIOUS TYPEHINTING WORK FOR ME LIKE BOSS
interface Command {};
class RubPlumbus implements Command {}
class SpitOnPlumbus implements Command {}
class PaintPlumbus implements Command {
    public function isBlue(): bool {return true;}
}
class PlumbusRubber {
    function __construct (PlumbusRepository $plumbusRepository) {}
    public function handle ($cmd) {}
};
interface Environment {
    public function db_host () : string;
    public function db_username () : string;
}
interface PlumbusRepository {}
final class MySQLPlumbusRepository implements PlumbusRepository
{
    function __construct (DBConnection $dbConnection) {}
}
class DBConnection {
    function __construct (string $host, string $username) {}
}

// ======================================================
// Run

$environment = new class implements Environment {
	public function db_host () : string { return 'foo'; }
	public function db_username () : string { return 'bar'; }
};
$dependencies = new class($environment) extends Dependencies { };

// $command = new RubPlumbus();
$command = new PaintPlumbus();
$router = new Router($dependencies);
$router->route($command);